Several publications and patent documents are cited throughout the specification in order to describe the state of the art to which this invention pertains. Each of these citations is incorporated by reference herein as though set forth in full.
The diagnosis of inflammatory bowel disease (IBD) is often achieved only months or years after the onset of symptoms. Several serological indicators of IBD have been identified; in general, they are antibodies directed against antigens expressed by organisms of the intestinal microbiome (1-4). For example, the anti-Saccharomyces cerevisiae antibody (ASCA) interacts with mannose epitopes of this yeast species and is present in 48% to 80% of patients with CD (5,6). In general, these markers are specific for IBD, but experience low sensitivity.
CD biomarkers can also be of value after the diagnosis is established, as measures of disease activity and predictors of outcome. The available serological markers have not proven useful in these contexts (7-13). Other serum and stool markers, such as C-reactive protein (CRP) and fecal calprotectin, are elevated in inflammatory and gastrointestinal diseases, but are not specific for IBD (14-19). The introduction of additional sensitive, specific, and noninvasive diagnostic markers may aid in the diagnosis of IBD, reduce patient risk and discomfort by reducing invasive testing, and accelerate the study of new treatments.
MicroRNAs (miRNAs) are short, noncoding RNAs that regulate target mRNAs via transcript degradation or translational repression. Cell- and tissue-specific miRNA expression profiles are altered in numerous disease states (20-30). The loss of all of the intestinal miRNA results in impaired barrier function and inflammation similar to IBD (31). With the exception of gastric and colorectal cancers (32,33), little is known regarding the function of miRNA in intestinal disease. Wu et al (34) profiled miRNA expression in colon biopsies in ulcerative colitis (UC), indeterminate colitis, infectious colitis, microscopic colitis, and irritable bowel syndrome. Significant changes were confirmed in 11 miRNAs in UC tissues when compared with normal controls, of which 5 were altered at least 2-fold. The authors focused on microRNA-192 (miR-192; 1.9-fold lower in active UC), showing that it localizes to colonic epithelia and is able to repress expression of the chemokine CXCL2 (MIP-2a) in a colonic epithelial cell line. They suggest that in UC, decreased miR-192 levels result in intestinal inflammation via increased CXCL2 secretion by epithelial cells. The same group has also investigated ileal and colonic miRNA expression, resulting in the identification of several miRNAs whose levels are altered in CD (35).
The recent discovery of circulating miRNAs possessing remarkable stability has prompted a number of studies investigating their potential merit as noninvasive biomarkers (36,37). Specific circulating miRNA profiles have now been described for various conditions, particularly cancer (36-41). In some cases, these circulating miRNA profiles are known to correlate with miRNA expression changes in the diseased tissue (41,42). Additionally, changes in circulating miRNA profiles may precede those of standard blood biomarkers (39,41), and several disease-specific profiles are known to possess both diagnostic and prognostic value (43,44). Taken together, these properties implicate miRNAs to be attractive, blood-based, noninvasive biomarkers.